Active noise reducing nozzle

ABSTRACT

A nozzle where the sector into which noise reduction is sought (the direction of populated areas) has a moving lip, driven by actuators in an oscillatory, periodic or sinusoidal motion, around the mid position, to and from the axis, so as to cause the shear layer to become more irregular and turbulent, thus enhancing scattering effects on the sound of internal sources, including back reflection into the jet, widening the directivity pattern and spreading the acoustic energy into a broader spectrum, so as to reduce the acoustic energy transmitted in these sensitive directions; the nozzle lip may also be corrugated, ondulated or have vortex generators, in the sector over which noise reduction is sought. In all other sectors, for which noise radiation is of no concern, even if enhanced, the nozzle lip is smooth and fixed, leading to a thin shear layer, across which sound is more easily, so that acoustic energy exits from the jet in these harmless directions. The active nozzle need only be actuated at times when noise reduction is needed, e.g. a take-off and landing; at all other times, when noise reduction is not needed, e.g. in cruise flight, the nozzle is not active, i.e. is fixed in the mid-position, to save actuator power, and wear and fatigue of moving mechanisms; also, this position, minimizes any thrust loss or increase in fuel consummation, in cruise flight.

REFERENCES—PAPERS

[0001] (1) L. M. B. C. Campos, “The spectra broadening of sound byturbulent shear layers. Part I: The transmission of sound throughturbulent shear layers”, Journal of Fluid Mechanics, Volume 89, part 4,pages 723-749, 1978.

[0002] (2) L. M. B. C. Campos, “The spectra broadening of sound byturbulent shear layers. Part II: The spectral broadening of sound andaircraft noise”, Journal of Fluid Mechanics, Volume 89, part 4, pages751-783, 1978.

[0003] (3) L. M. B. C. Campos, “Sur la propagation du son dans lesécoulements non-uniformes et non-stationaires”, Revue d'Acoustique,number 67, pages 217-233, 1983.

[0004] (4) L. M. B. C. Campos, “Modern trends in research on waves influids. Part I: Generation and scattering by turbulent and inhomogeneousflows”, Portugaliae Physica, Volume 14, Fasc. 3-4, pages 121-143, 1983.

[0005] (5) L. M. B. C. Campos, “On waves in gases. Part I: Acoustics ofjets, turbulence and ducts”, Reviews of Modern Physics, Volume 58, pages117-182, 1986.

[0006] (6) L. M. B. C. Campos, “Effects on acoustic fatigue loads ofmultiple between a plate and a turbulent wake”, Acoustic, 76, pages109-117, 1992.

[0007] (7) L. M. B. C. Campos, “On the correlation of acoustic pressureinduced by a turbulent wake on a nearby wall”, Acoustic—Acta Acustica,Volume 82, pages 9-17, 1996.

[0008] (8) L. M. B. C. Campos, “On the spectra of aerodynamics noise andaeroacoustic fatigue”, Progress in Aerospace Sciences, Volume 33, pages353-389, 1997.

[0009] (9) L. M. B. C. Campos, J. M. G. S. Oliveira & M. H. Kobayashi,“On sound propagation in a linear shear flow”, Journal of Sound andVibration, Volume 95, pages 739-770, 1999.

[0010] (10) L. M. B. C. Campos, P. G. T. A. Serrão, “On the acoustics ofan exponential boundary layer”, Philosophical Transactions of theSociety, Volume A356, pages 2335-2378, 1999.

[0011] (11) L. M. B. C. Campos, A. Bourgine & B. Bonomi, “Comparison oftheory and experiment on aeroacoustic loads and deflection”, Journal ofFluids and Structures, Volume 13, pages 3-35, 1999.

[0012] (12) L. M. B. C. Campos & M. H. Kobayashi, “On the reflection andtransmission of sound in a thick shear layer”, Journal of FluidMechanics, Volume 424, pages 303-306, 2000.

REFERENCES—PATENTS

[0013] (1) E. N. Poulos, “Noise Abatement Moans”, U.S. Pat. No.2,934,889, May 3, 1960

[0014] (2) Y. Y. Sheorcen et al., “Enhaust eductor cooling means”, U.S.Pat. No. 5,265,408, Nov. 30, 1993

[0015] (3) S. H. Zysman et al., “Double labed mines with major and minorRobos”, V.S. Past U.S. Pat. No. 5,638,675, Jan. 17, 1997

[0016] (4) M. P. Presz, Jr. et al., “Alternating libed mined/ejectorconcept suppressor, U.S. Pat. No. 5,984,472, Mar. 23, 1999.

[0017] (5) J. M. Seiner, et al. “Jet nozzle having centerbody forenhanced exit area mining”, U.S. Pat. No. 5,924,632, Jul. 20, 1999.

[0018] (6) J. P. Nikkanen et al., “Inlet and out let, module for a heatexchanges for a flew paths per working, medium gases”, U.S. Pat. No.6,058,696, May 9, 2000.

[0019] (7) J. M. Seiner, et al., “Undulated nozzle for exhanced exitarea mining”, U.S. Pat. No. 6,082,635 Jul. 4, 2000.

SCIENTIFIC BACKGROUND

[0020] The present patent concerns a nozzle design which reduces jetexhaust noise. Among the sources of noise of turbojet and turbofanengines, that corresponding to the jet exhaust is one of the mostimportant. The jet exhausts into the atmosphere, where ambient air movesat much lower speed, particularly in low-speed flight phases, liketake-off and landing; these flight phase are of most concern regardingnoise around airports, and are subject to ICAO (International CivilAviation Organisation) noise certification rules, as well as additionalrestrictions at some airports.

[0021] The jet exhausting into ambient air forms a shear layer, acrosswhich the velocity changes from the jet speed to the ambient speed. Thenoise from sources inside the jet is transmitted to the exterior acrossthis shear layer, and this process can change the intensity, directivityand spectrum of sound, thereby reducing the noise disturbance outside.In the case of a turbofan, there are two co-axial jets, and thus twoshear layers; the noise from sources in the inner jet is transmitted tothe exterior across two shear layers, with possible multiple internalreflections, leading to greater scattering effects and lower noise. Thevarious mechanics of noise reduction are explained next, by startingwith simple models of the shear layer, and elaborating themstep-by-step, until close similarity to a real shear layer is achieved.

[0022] The simplest model is a vortex sheet, i.e. a surface across whichthe velocity changes abruptly from the jet speed to the ambient speed.This model would apply if the wavelength of sound was much larger thanthe thickness of the shear layer, and the scale of irregularities of theshear layer and if no turbulence were entrained with the shear layer;and if no turbulence were entrained with the shear layer. All theserestrictions will be removed later. Staying for the moment with a planevortex sheet, it is clear that a sound source inside the jet will emitan acoustic wave, incident upon the vortex sheet, giving rise toreflected and transmitted wave. The existence of a reflected wave, meansthat not all acoustic energy is transmitted across the shear layer, sothere is a reduction in acoustic intensity outside the jet. Thetransmitted wave is not radiated in all directions, i.e. there is a‘zone of silence’ outside the jet, where there are only evanescentwaves. Thus the transmitted sound field has a reduced intensity comparedto the direct sound field of the source, and also a modified directivitypattern including one “zone of silence” or two (the latter for jet machnumbers exceeding two).

[0023] Lets elaborate the model a little more, and assume that thevortex sheet is not flat but rather is irregular. This will apply if thewavelength is still much larger than the thickness of the shear layerbut is not much larger than the scale of its irregularities; for themoment, turbulence or eddies entrained with the shear layer are notconsidered yet. The incident sound wave originating from the source nowhits the irregular vortex sheet at different, and gives rise locally toreflected and transmitted waves. Since these waves are no longer inphase, there can be destructive interference in the transmitted soundfield, reducing the noise level outside the jet, compared with a flatvortex sheet between the same media. Also, the irregular vortex sheetcan transmit sound into what would be the ‘zone of silence’ of a flatvortex sheet, because local scattering conditions may allow this; thusthe transmitted acoustic energy is spread over a wider range ofdirections, by an irregular vortex sheet, as compared with a flat vortexsheet, further modifying the directivity, and reducing the intensity ofradiation.

[0024] It should be borne in mind that the irregular vortex sheetseparating the jet from ambient moves at a convection velocityintermediate between the two. When sound is scattered from a movingsurface, its frequency is changed by the Doppler effect. Resides theDoppler shifted frequency of the source, harmonics at other frequenciesmay appear. Thus a moving, irregular vortex sheet further reduces thenoise relative to a static irregular vortex sheet, because the acousticenergy is spread over more frequencies.

[0025] So far it has been assumed that the moving irregular vortex sheetrepresenting the shear layer has a fixed shape; actually, real jet shearlayers are turbulent, and thus should be represented by a randomlyirregular moving vortex sheet, if the wavelength is very large comparedwith the thickness of the shear layer vortex sheet with randomlychanging shape causes random changes in the direction of the transmittedwave, and thus scatters sound over a wider range of directions andcauses more interference between wave components; also a randomlyirregular moving vortex sheets causes random Doppler shifts, thusspreading the acoustic energy over a wider spectrum. The three effects,viz: (i) more interference between wave components, (ii) widerdirectivity pattern and (iii) broader spectrum, all contribute to reducethe acoustic intensity received on average on each direction and theeach frequency outside the jet.

[0026] It is appropriate to introduce at this stage the spectraldirectivity defined as the acoustic power received per unit frequencyand unit solid angle.

dW=I(θ,φ,ω) sin θdθdφdω.

[0027] It has already been explained why a randomly irregular movingvortex sheet reduces the spectral directivity and total acoustic powerreceived from the source. The explanation has been based on threescattering effects: (i) wave interference; (ii) wider directivitypattern; spectral broadening. These effects have been demonstrated forscattering by a randomly irregular moving interface, which is anadequate model of a shear layer if the wavelength is much larger thanthe thickness of the shear layer. We shall now lift this last remainingrestriction.

[0028] For sound of arbitrary, i.e. smaller wavelength, the shear layerno longer appears as a discontinuity of velocity between the jet andambient medium, but rather as a smooth velocity change or shear flow.The transmission of sound through this shear flow demonstratesscattering effects, like for a vortex sheet, with the additionalpossibility of sound absorption by the flow, at critical points wherethe Doppler shifted frequency vanishes. This is a further noise reducingmechanism.

[0029] A real shear layer is not only a shear flow, but also entrainsturbulence and eddies. The effects of turbulence and eddies on thescattering of sound are similar to those of a randomly irregular movinginterface, in the sense that: (i) there is backscattering, i.e. some ofthe acoustic energy is scattered back into the jet, and thus does notreach the ambient medium; (ii) there is a wider directivity pattern,because sound is deflected into directions which might not be present inthe incident wave; (iii) there is spectral broadening, because theconnection of sound by turbulence and eddies causes random Dopplershifts; (iv) the changes in direction of propagation and frequency causeinterference between sound waves. The ensemble of four effects (i) to(iv), plus possible (v) sound absorption at critical layers is called“scattering effects” in what follows. It is clear that these scatteringeffects reduce the noise transmission from a jet to the exterior.

[0030] The preceding description applies (FIG. 1) to the noise sourcesof a turbojet engine, as concerns the transmission of sound from theinterior of the jet to the ambient across the shear layer. In the caseof turbofan engines (FIG. 2); there is a hot high-speed core jet withburned gases, surrounded by a cooler, lower-speed by-pass flow of air,and thus there are two concentric shear layers: (i) and inner shearlayer between the core jet and the by-pass flow; (ii) an outer shearlayer between the by-pass flow and the ambient atmosphere. The hot,high-speed core jet is the noisiest, but sound from sources in the corejet has to be transmitted across two shear layers to be receivedoutside, thus increasing “scattering effects”. The sound from sources inthe by-pass flow has to be transmitted only across one shear layer, butthe sources are weaker than in the core jet. There can be multipleinternal reflections between the two shear layers; (i) for sound fromsources in the by-pass flow; (ii) for sound from sources in the corejet, transmitted across the inner shear layer to the by-pass flow. Allthese mechanisms enhance the “scattering effects” in a turbofan exhaust,compared with a turbojet, and help to explain its lower noise levels.

INNOVATIVE ELEMENTS

[0031] The noise of exhaust jets can be reduced by enhancing the“scattering effects” of the shear layer issuing from the nozzle lip, bymaking it more irregular in two ways:

[0032] (A) by having a corrugated or undulated nozzle;

[0033] (B) by having the nozzle lip move in an oscillatory manner drivenby actuators.

[0034] The option (A) is what may be called a “passive” nozzle; severalpatents have suggested “passive” nozzles with lobes and corrugations. Wewill propose some novel improvements. The option (B) may be called a“active” noise-reducing nozzle, and is an entirely new feature of thepresent patent we will considering the “scattering effects” of current“passive” nozzles, before proceeding to “improved passive nozzles” and“active nozzles”.

[0035] A type of passive nozzle in use for several decades, is themulti-lobe ejector nozzle (FIG. 3). The lobes reduce the maximum size ofeddies in the jet, thus reducing noise. They also produce a moreirregular shear layer, which enhances scattering effects, and thusreduces sound transmission to the exterior of the jet. The multi-lobeejector nozzle is acted by a force due to the jet, and thus reducesthrust. For the same fuel born, a lower thrust mean higher specific fuelconsumption. Note that the penalties of thrust loss and increased fuelconsumption apply to all flight phases, including cruises; the noisereduction is needed when flying near an airport, i.e. only at take-offand landing.

[0036] Another type of passive nozzle (FIG. 4) has undulations, orcorrugations, or vortex generators around its circumference. It does notreduce significantly the size of the largest eddies in the jet, and hasa lesser negative effect on thrust and fuel consumption than themulti-lobe nozzle. It does produce a more irregular shear layer than thenozzle with a smooth lip, and thus increases scattering effects andreduces sound transmission to the exterior of the jet. It should benoted that the vortices shed by the nozzle are noise sources, and thusradiate sound, besides scattering sound from sources inside the jet.

[0037] In many applications, it is not necessary to reduce noisetransmission in all directions, but only some. For example, the ICAOnoise certification rules concern only ‘fly over’ and ‘side line’ noisefor the take-off and landing phases of flight. Thus it is important toreduce sound transmission in a sector downwards, and it is only in thissector that nozzle lip treatment is needed (FIG. 5) to produce a moreirregular shear layer, and increase scattering effect. The “improvedpassive” nozzle, with non-aximometric lip treatment only in the downwardsector ACR (FIG. 5) is an advance over the nozzle (FIG. 4) withtreatment over the whole periphery, for several reasons:

[0038] it allows sound to be transmitted more easily out of the jet intothe ‘harmless’ directions in the upward sector {overscore (ADR)},reducing the acoustic energy in the jet;

[0039] it is equally effective in reducing sound transmission in thesector {overscore (ACB)} where the noise disturbance should be avoided.

[0040] The combination of less acoustic energy in the jet, and equallyeffective scattering in the sector {overscore (ACB)}, results in lesssound transmission for “the improved passive” nozzle with sectorial liptreatment (FIG. 4) than for conventional passive nozzle (FIG. 4). Thispassive nozzle with sectorial lip treatment is an innovation of thepresent patent. It is more effective at noise reduction than theconventional nozzle, and besides, it is simpler and cheaper to build,because lip treatment is applied only over part of the circumference;for the same reason it is also lighter, and affects less thrust and fuelconsumption.

[0041] So far consideration has been given only to passive nozzles, withlip treatment. Another way to increase the irregularity of the shearlayer, and thus increase scattering effects and reduce soundtransmission, is for the nozzle lip (FIG. 6) to oscillate up-and-down,e.g. periodically or sinusoidally, driven by activators. This “activenozzle” need only have a moving lip over the arc {overscore (ACR)} ofdirections for which noise reduction is sought. The “active” nozzle hasthe advantadge that the moving lip need be actuated only during thetake-off and landing phases of flight, when noise reduction is sought.During other phases of flight, e.g. cruise, the nozzle lip is kept fixedin the normal position, saving actuator power. This cruise configurationis similar to a fixed nozzle, so there are no penalties on thrust lossor fuel consumption.

[0042] The “active nozzle”, or nozzle with a moving lip, may have eithera smooth lip (FIG. 6) or a corrugated (FIG. 7) one. If a corrugated lipis chosen (FIG. 8), then the sound scattering effect is enhanced, sinceboth the corrugated lip and the lip motion contribute to make the shearlayer more irregular, in the take-off and landing phases; in the cruisephase, with lip motions deactivated, the corrugated lip section stillmay affect thrust and fuel consumption.

[0043] If the nozzle lip is smooth (FIG. 6), then in cruise flight, withfixed lip, there is no thrust loss or increase in fuel consumption; attake-off and landing, the lip motion will enhanced scattering effectsand reduce sound transmission. If this noise reduction is enough, thenthe active nozzle with smooth lips is the best solution because:

[0044] it has no effect on cruise thrust or fuel consumption;

[0045] actuation is needed only in the take-off and landing phases offlight, reducing power requirements, structural fatigue of moving parts,etc.

[0046] the moving lip needed only be over the sector (‘flyover’ and‘sideline’) where noise reduction is sought.

[0047] This type of nozzle is the simplest solution, because it producesa more irregular shear layer only when needed (at take-off and landing)and in the directions sought (to reduce the noise disturbance in thefly-over and sideline positions around the airport).

BRIEF DESCRIPTION

[0048] Consider a jet issuing from a nozzle, which may be circular (FIG.9), rectangular (FIG. 10) or any other shape. Consider the sector (FIG.9) {overscore (ABC)} comprising the direction of populated areas, wherenoise reduction is sought. Assume that all other directions are notpopulated, so there is no need to reduce noise in those directions, andno harm in re-directing some of the acoustic energy in those directions.Then the lip of the nozzle over this sector will be made to move, to andfrom the axis, in an oscillatory, periodic or sinusoidal more, by usingappropriate actuators, and dividing the lip into sections with joints asnecessary. The resulting more irregular shear layer will enhancescattering effects, and reduce sound transmission into the directionswhere noise reduction is sought.

[0049] The nozzle lip will be actuated only at those times or stages offlight when noise reduction is sought, e.g. take-off and landing, toreduce the noise disturbance around airports. At all other times orstages of flight, e.g. cruise, the nozzle lip is not actuated, savingpower and avoiding structural fatigue of moving components.

[0050] If the nozzle lip is smooth, then in the fixed ‘cruise’ positionthe nozzle shape is unchanged, and there is no thrust loss or increasein fuel consumption. The moving section of the nozzle lip may also becorrugated, to increase further the scattering effects and providegreater noise reduction. In the case of turbofan (FIG. 9) the sectors ofthe nozzle periphery which are (i) “active” or actuated and (ii) passivebut corrugated, may coincide or not. Also one lop could be “active” andthe other “passive”, and either could be smooth or corrugated, in anycombination.

PREFERRED EMBODIMENTS

[0051] Three embodiments will be described: (i) a jet engine withcircular nozzle; (ii) a turbofan engine with two co-axial circularnozzles; (iii) two or more engines with a common rectangular nozzle.

[0052] The first embodiment is a jet engine with a circular or ovalizednozzle (FIGS. 6 and 7). The sector corresponding to populated areasaround the airport is {overscore (ACB)}. For the “active noise-reducing”nozzle this sector moves to and fro the axis, driven in an oscillatory,or periodic or sinusoidal manner by actuators; the sector {overscore(ACB)} may also be divided into ‘petals’ or ‘sections’ with appropriatehinges. The actuators are powered only during the phases of flight whennoise reduction is sought, e.g. take-off, landing and possibly initialclimb and final descent. The sector {overscore (ACB)} of the nozzle lipcould have or not (FIG. 8) corrugations, undulations or vortexgenerators, to enhance scattering effects further and reduce more thesound transmission. The same methods could be used in other sector, e.g.to reduce noise radiation from the engines to the cabin in cruiseflight.

[0053] The second embodiment concerns a turbofan engine (FIG. 9) withconcentric circular or ovalized nozzles for the core jet and by-passflow. The sectors for noise reduction could be the same or different forthe by-pass flow {overscore (ACB)} and core jet {overscore (A′C′B′)}.The nozzle of the by-pass flow should be 2active2 at the stages offlight requiring noise reduction, to reduce transmission of sound fromboth the by-pass flow and core jet; it could have lip corrugations ornot. The nozzle of the core jet could be “passive” or “active” and besmooth or corrugated. Thus there would be plenty of scope for trade-offsamong noise reduction, complexity and weight, thrust and fuelconsumption penalties. Two active nozzles both with corrugated lipswould give the greatest noise reduction and also the biggest penalty incomplexity, weight, thrust and fuel consumption. These penalties wouldbe reduced by going for smooth lips and making only one nozzle active,say the outer nozzle whose shear layer scatters both core jet andby-pass flow noise.

[0054] The third embodiment concerns two or more engines in a nacellewith a rectangular nozzle (FIG. 10). It may be assumed that the lowerlip AB will be “active” and may or may not have corrugations, to reduce‘fly-over’ nozzle. The upper lip {overscore (CD)} will be smooth andfixed, since there is no need to reduce sound transmission upwards, andthere is no harm even in increasing it, to reduce the acoustic energy inthe jet. The side panels {overscore (CA)} and {overscore (DB)} may bepassive or active, and may be smooth or corrugated, depending on theneed or not for noise reduction. For example, if the fuselage is on theside {overscore (CA)}, an active and/or corrugated panel would reduceaerial (as distinct from structural) transmission of sound from theengine to the cabin; if the panel {overscore (DB)} lies in a sector of‘sideline’ noise, it may need to be active and/or corrugated, to reduceside-line noise. In cruise flight, the panels {overscore (AB)} and{overscore (BD)} would become passive, but {overscore (AC)} could remainactive if cabin noise reduction was an issue.

[0055] The three embodiments described concern aircraft applications.However, similar ideas apply to other jet exhaust installations, e.g. inships, power plants, land vehicles, industrial installations, etc. Inall these cases an active nozzle lip, with or without corrugations, maybe used to reduce sound transmission in directions where noise reductionis sought; a passive and smooth nozzle lip is used in all otherdirections. The “active” nozzle is used only at times when noisereduction is needed, e.g. at night, and is switched-off to save powerand wear at other times.

[0056] From the point-of-view of construction, a “improved passive”nozzle with lip treatment only over a fraction of the periphery, wouldbe built like a conventional passive nozzle, with similar lipundulations or vortex generators. An “active” nozzle requires that thepart of the periphery of the nozzle used for noise reduction be movableto and from the axis, either as a single piece or a set of segments orpetals e.g., as already used in variable-area and thrust-vectoringnozzles. In a similar way, actuators would be used to drive the movingelements of the active nozzle; the alternative would be to leave themoving elements in free motion. In the latter case, the free motion ofthe nozzle elements would be determined by the aerodynamic forces aroundthe nozzle. In order to give the moving elements of the active nozzle aprescribed motion, optimized noise reduction is sought; a passive andsmooth nozzle lip is used in all other directions. The active nozzle isused only at times when noise reduction is needed, e.g. at night, and isswitched-off to save power and wear at other times.

[0057] From the point-of-view of construction, a “improved passive”nozzle with lip treatment only over a fraction of the periphery, wouldbe built like a conventional passive nozzle, with similar lipundulations or vortex generators. An “active” nozzle requires that thepart of the periphery of the nozzle used for noise reduction be movableto and from the axis, either as a single piece or a set of segments orpetals e.g., as already used in variable-area and thrust-vectoringnozzles. In a similar way, actuators would be used to drive the movingelements of the active nozzle; the alternative would be to leave themoving elements in free motion. In the latter case, the free motion ofthe nozzle elements would be determined by the aerodynamic forces aroundthe nozzle. In order to give the moving elements of the active nozzle aprescribed motion, optimized to maximize noise reduction, the actuatorswould be commanded by a control system. The control law used could beeither calculated for the flight conditions, or be based on sensorsignals or combination of both.

What is claimed:
 1. a nozzle whose perimeter can be divided into sectorsof two types: sectors I for which noise reduction is sought, becausethey correspond to the directions of populated areas, into which soundradiation should be reduced, and sectors II corresponding to directionsin which there is no population or noise sensitive beings or structures,so that no noise reduction is sought, and even increased sound radiationmay be harmless, so that different treatment is given to the two typesof sectors, namely: in the sectors I, where noise reduction is sought,the nozzle lip is active, i.e. moves in and out relative to the axis, inan oscillatory motion, driven by actuators commanded by a control systemso as to make the shear layer more irregular and turbulent, or left infree motion, thus scattering back a larger fraction of the sound fromsources inside the jet, and spreading the sound which is transmittedoutside over a wider range of directions and frequencies; and also, inthe sectors I where noise reduction is sought the nozzle lip may besmooth, or may have corrugations, undulations and/or vortex generators,to enhance the sound scattering effects and reduce sound transmissionfurther, whereas in the sectors II where noise reduction is not soughtand increased sound radiation is harmless, the nozzle lip is smooth andfixed, to produce a thin shear layer, which allows as much as possibleof the acoustic energy in the jet to exit in harmless directions, withthe operation of the nozzle being scheduled over time, so that: whennoise reduction is needed, the movable nozzle lip sectors are driven bythe actuators in the most suitable way, or left in free motion, toachieve maximum noise reduction; whereas when noise reduction is notneeded, the movable nozzle lip sections are fixed in the position whichminimizes thrust loss and causes no increase in fuel consumption, alsosaving actuator power, wear of mechanisms and fatigue of structures, andfurthermore, similar mode of operation applying to any number ofnozzles, coaxial or not, circular or not, including nozzles of nacellescontaining several engines, and applications to any type of vehicle(air, land, sea) in a moving, fixed or deployable installation(powerplant, factory, etc . . . )